The demo is quite fun, but only 2 levels is not enough to really sell me on the game.
Another 2D top down shooter that I've found interesting is a Japanese game called "Imperishible Night", which is one of the oddest games I've ever played.
The appeal of the game lies in it's constant boss-battles, where there are ENORMOUS quantities of deadly shots flying around. The challenge is mostly in figuring out the subtle patterns, but there's a lot of reflexes involved as well.
The plot of the game is very odd (shrine maidens dueling to end eternal winter?
) and there's a lot of indecipherable Japanese dialog, but the gameplay is like nothing else.
Here's a video of one of the harder levels, it's quite impressive. Be aware that the video runs in fast-motion until the boss appears, that's not the normal game speed.
http://www.youtube.com/watch?v=BDBT2gGKlDk
There's also a demo that you could check out here:
http://www.shrinemaiden.com/MKIM.htm